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Alice & Bob

Who Are Alice & Bob?

Who Are Alice and Bob?

Alice and Bob are fictional characters who are often used to describe problems or dilemmas in cryptography or communications protocols. Alice and Bob are typically trying to send and receive data between each other such as a simple message or a cryptographic key. In most scenarios, a number of different characters are attempting to attack their communications either simply by passively listening in or launching malicious attacks.

Additional Characters

As Alice & Bob’s problems, discussions, and dilemmas grew more complex over time, other fictional characters were introduced to help explain various scenarios. Some of these characters are simply a new generic character with a name that begins with a new letter of the alphabet such as Carol and Dave while others have some sort of illiterate name to help describe their role such as Craig the password cracker or Grace the government agent.

Eve

Eve was introduced as a passive attacker who was listening in or “eavesdropping” on communications between Alice and Bob in an attempt to compromise any private or secret information such as a secret password or private key.

Eve would easily be able to successfully compromise a symmetric private key that was shared but with the use asymmetric key pair cryptography, Eve is unable to successfully eavesdrop on any communications between Alice and Bob.

A common attack involving Eve might be a compromised password to gain access to a bitcoin wallet. One of the reasons why it is so important to not store or share your seed phrase or private keys online is because “Eve” might be able to access it and steal your bitcoin.

Mallory

Mallory is a malicious attacker who is attempting to modify, substitute or replay old messages to trick either Alice or Bob. Unlike Eve who is only passively listening in and trying to gain secret information, Mallory is actively trying to trick and deceive with false information. A common attack that might involve Mallory is a man-in-the-middle attack.

Judy

Judy is sometimes used as an arbiter or mediator between two parties who do not agree on something. This could be someone who holds 1 of 3 keys in a multisig wallet arrangement in the event that Alice and Bob do not agree on how funds should be spent.